Okay, perhaps this is a stupid question, but it’s been bugging me all day.
Exactly why do onions have layers? What is the evolutionary advantage for the onion to have layers as opposed to not having layers?
Cut some cattails off near or at the ground. Look at the cross section. Do you see how every blade of the plant goes all the way down to the roots?
Well an onion is like that except that the blades all widen at the bottom to form the onion. The layers of the onion, or any other bulb for that matter, correspond to the leaves, which is all a blade is.
The bulb is a great way for the plant to store sugars and other foods it needs to hang on through the winter monthes and gives it a leg up, come spring.
It makes an onion bulb because there is no" down side" to making one. Unless , of course, you consider picking it a “down side”
I wasn’t going to post this lest it make me look like an idiot, but here goes:
I believe the onion bulb grows by adding layers, much like how a tree trunk grows by adding layers. The actively growing cells are in the center, and they grow by adding another hard layer of onion. Those layers are gradually pushed out, towards the outer surface of the onion as the bulb grows.
And it does that because that’s the only way it can grow. Harder exteriors make for greater water/nutrient retention, protection, and structural integrity, which is important, but it makes growth a little harder. It’s not like a sac that could just expand. So it grows layers.
If I’m horribly off track, someone please help me. It’s been at least five years since I took botany.
An onion is a bulb. which is a modified version of a stem - the layers are modified leaves; this is different from:
corms(crocus)which are modified stem-bases or roots
tubers(potato) which are modified roots
Corms and tubers usually do not display layererd internal structure (or if they do it is usually in a similar form to annual growth rings in a tree trunk).
Leeks (closely related to onions) demonstrate how a bulb forms; the growing bud is protected deep within the centre of the plant and new leaves emerge from the centre. In order to destroy the plant by eating the bud, an animal would have to munch through quite a lot of outer layers (which, in the case of the onion, contain pungent substances specifically to discourage this).
They’re like ogres…
(Sorry, couldn’t help it)
I always assumed they grew in layers to make it easier for me to put them on my bagel…
Then why doesn’t cream cheese grow in layers too, huh smartypants??
That makes sense. Though it is interesting, that being the case, that many humans cutivate onions specifically because of the taste (if not the eye-watering aroma). Of course,the Onion doesn’t care, as it isn’t going extinct anytime soon.
Indeed, the same is true of many foods that humans choose to eat, particularly herbs and spices - the plants developed chemicals that would discourage specific pests (not always humans or even mammals) from eating them, but humans developed a liking for them.
As already noted in posts above, the layers of an onion are modified leaves that together with a modified section of stem, form a bulb.
The purpose of the bulb is to allow the plant to store nutrients and water and this in turn allows such plants to take advantage of seasons that other plants cannot. For example, in deciduous woodland a bulb plant is able to get put out leaves and take advantage of the spring before the trees put it into the shade. Bulbous plants can flower early in spring - one of the features that makes them popular with gardeners.
Of course, as the bulb contains a concentration of nutients, the bulb needs to be protected from animals. Consequently many bulbs are poisonous or at least foul smelling/tasking. Humans, being strange animals, have developed a taste for some of these fould smelling and/or tasting bulbs such as onions and garlic and have breed them as food crops.
I wonder if it is the case that one typically finds bulbous plants in temperate rather than equatorial climates?
Bulbs are most common in climates where there are distinct wet and dry seasons, but they can be found pretty much everywhere.